Lewis rats will be immunized with encephalitogenic peptides 68-85 and 68-88 from guinea pig myelin basic protein. Affinity chromatography will be used to obtain purified anti-peptide antibodies from single rats. The purified antibodies will be characterized by immunoelectrophoresis, sodium dodecyl sulfate polyacrylamide gel electrophoresis and isoelectric focusing. Rabbits or Lewis rats will be immunized for the production of anti-idiotypic antibodies. Following absorption of the anti-idiotypic antisera with pooled rat immunoglobulin, the anti-idiotypic antisera will be assessed for 1) the ability to inhibit binding of radiolabeled antigen to the rat antibody used for immunization and to anti-peptide antibodies from a large number of other rats, 2) specificity for VH or VL regions of the anti-peptide antibody used for immunization, and 3) the ability to alter the function of T-lymphocytes involved in the manifestations of experimental allergic encephalomyelitis in vivo and in vitro.